In the human eye, the tear film covering the ocular surfaces is composed of three layers. The innermost layer in contact with the ocular surface is the mucus layer. The mucus layer is comprised of many mucins. The middle layer comprising the bulk of the tear film is the aqueous layer. The aqueous layer is important in that it provides a protective layer and lubrication to prevent dryness of the eye. Dryness of the eye can cause symptoms such as itchiness, burning, and irritation, which can result in discomfort. The outermost layer is comprised of many lipids known as “meibum” or “sebum.” This outermost lipid layer is very thin, typically less than 250 nm in thickness. The lipid layer provides a protective coating over the aqueous and mucus layers to limit the rate at which these underlying layers evaporate. A higher rate of evaporation of the aqueous layer can cause dryness of the eye. Thus, if the lipid layer is not sufficient to limit the rate of evaporation of the aqueous layer, dryness of the eye may result. The lipid layer also lubricates the eyelid during blinking, which prevents dry eye. If the lipid layer can be improved, the rate of evaporation is decreased, lubrication is improved, and partial or complete relief of the dry eye state is achieved.
One environment which can contribute to dry eye is an airplane cabin. The interior of a pressurized airplane cabin has very low relative humidity, such as between 10 and 20%. Long airplane flights can severely irritate the eyes and cause dry eye.
Dry eye can also be caused by a condition known as meibomian gland dysfunction (MGD). Known treatments for MGD generally apply significant heat in order to melt, loosen, or soften of obstructions or occlusions in the meibomian glands. Regarding electrical heaters, one known eye treatment is described in U.S. Patent Pub. No. 2007/0060988. The heater it describes applies heat by using an electrical signal requiring the use of a thermocouple and sophisticated feedback control system to monitor and adjust the electrical signal to maintain heat between 43 and 47 degrees C. to one eye for between 1 and 10 minutes. Furthermore, the device uses a screw to adjust pressure on the eye. Because it requires 1) a threaded shaft or screw adjustment, 2) elevated heat, and 3) precise thermal regulation independent of temperature, the time of treatment, actual temperature, and pressure on the eye must be administered and monitored by a medical physician or technician to avoid burning the eyelid or damaging the eye itself. Another heater is described in U.S. Pat. No. 4,261,364. The heater it describes uses a battery operated surgical heater that warms a compress resembling an eye patch for post-ophthalmic surgery patients. The heater is strapped to a surgical compress that applies heat to a patient's eye socket. Since the heater 1) is in molded plastic not integrated with the compress, 2) is battery operated, 3) uses wiring for a heating element, and 4) heats a compress rather than an eyelid, the result is an uncomfortable, uncontrolled heat source that cannot carefully control the temperature that reaches the eyelid itself. Because of these factors, the time of treatment, actual temperature, and pressure on the eye must also be administered and monitored by a medical physician or technician to avoid burning the eyelid or damaging the eye itself.
In the following description, the use of the same reference numerals in different drawings indicates similar or identical items. Moreover unless otherwise noted, the word “coupled” and its associated verb forms include both direct connection and indirect electrical connection by means known in the art, and unless otherwise noted any description of direct connection implies alternate embodiments using suitable forms of indirect electrical connection as well.